A dispersion is a mixture in which one phase is dispersed in another, continuous phase, of a different composition or phase. An emulsion is a dispersion comprising two immiscible liquids, one of which is dispersed as droplets (internal phase) in the other (continuous or external phase). Thus, all emulsions are dispersions, but not all dispersions are emulsions. Stable emulsions are those which are unable to resolve themselves into their constituent phases without some form of mechanical or chemical treatment.
In the petroleum industry, various operations including, but not limited to, exploration, production, refining and chemical processing of hydrocarbons including, but not limited to, crude oil, gas and their derivative products, routinely produce mixtures and dispersions of oil and water. Such mixtures typically also contain other compounds, including but not limited to, waxes, asphaltenes, various salts, suspended materials, biological surface active material from the ground, added surface active corrosion/scale inhibiting reagents, etc., which may vary from location to location. In addition, synthetic and natural surfactants, produced either in-situ or added in enhanced oil recovery techniques such as akali-surfactant (AS) and alkali-surfactant-polymer (ASP) floods, can cause phase separation issues. Along with the presence of these other compounds, high shear and mixing forces cause these oil and water mixtures to form dispersions and relatively stable emulsions. Some such emulsions are water in oil emulsions, commonly referred to in the petroleum industry as “regular” emulsions, in which oil is the continuous phase. Others are oil in water emulsions, commonly referred to in the petroleum industry as “reverse” emulsions, in which water is the continuous phase.
“Breaking” oil-water emulsions means separation of the oil and water phases. The term “breaking” implies that the emulsifying films around the droplets of water or oil are “broken” so that coalescing may occur and result in separation of the oil and water phases over time, for example, by gravitational settling. For example, demulsifiers describe the class of agents which break or separate an emulsion, whether normal or reverse, into its constituent phases. Clarifiers describe compounds which are applied to break emulsions and separate the oil phase from the water, thereby, making the water “clearer.” There is known to be some overlap in the types of compounds which effectively demulsify and those which clarify, i.e., some compounds are useful for both demulsifying and clarifying oil-water emulsions and dispersions.
During the production phase of an oil well, a large quantity of water may be pumped down into the ground via one or more injector wells to push oil in the underground formation toward the producing well and out of the ground. As the wells age, formation water is produced from the well in combination with the oil. Further, in many secondary and tertiary oil recovery techniques such as steam flooding, oil extraction from tar/oil sands and steam assisted gravity drainage (SAGD), large amounts of water are used to recover oil. In such circumstances, the oil typically comes out of the ground as an emulsion. To break this emulsion, i.e., separate the water from the oil phase, demulsifiers such as polyalkylene glycols (PAGs), block copolymers of polyethylene oxide) (PEO) and poly(propylene oxide) (PPO), and alkylphenol resin alkoxylates are generally used. In some cases water clarifiers are also added to the crude emulsion stream.
Once the emulsion is separated into an oil fraction and a water fraction, the produced water fraction (i.e., “produced water”) may contain about 1000 parts per million (ppm) oil entrained in the water phase. In other words, a “reverse” i.e., oil in water, emulsion is formed. This emulsion appears anywhere from brown to black, depending on the amount of impurities present. Such produced water may be generated in huge quantities (i.e., up to millions of gallons per day), and is either reinjected into the formation, or disposed of into the ocean. Governmental regulations, such as the US Clean Water Act and the US EPA Code of Federal Regulations in the United States, require reduction of the amount of oil content down to very low levels before the produced water may be discharged. Although the amount of oil permitted in discharged water under such regulations varies from jurisdiction to jurisdiction, the standard is generally very low, i.e., usually much less than 100 ppm oil in water. Further with the increasing cost and regulation on fresh water use, low levels of oil are demanded for water reuse. The practice of reducing the oil in water from the naturally occurring amount to below 50 ppm is commonly known as “clarification,” and is simply the breaking of the reverse emulsion. Clarification of such demulsified oilfield water typically involves use of acrylate polymers, cationic polymers, cationic polyelectrolytes, and water-soluble amphiphilic polymers to flocculate suspended oily and particulate materials and, thereby, obtain clear(er) water.
Successful selection and use of effective polymer compounds to demulsify and clarify oil-water emulsions formed during petroleum industry operations is very complex because whether or not a particular polymer will work depends on many factors including, but not limited to: the geology and location of underground oil-containing formations, the source of water, the nature of suspended solids, the type of oil, the nature of other reagents used, etc. Thus, there is no one solution for the practice of demulsification and clarification of oilfield emulsions. Depending on individual oilfields and the conditions involved, different polymers will provide optimum performance in different locations.
The prior art includes many patents and general literature relating to demulsification and clarification of oil-water dispersions and emulsions produced by petroleum industry operations. However, none disclose the use of anionic polymers based on acrylate monomers and their esters, which are hydrophobically modified or modified with surfactant-like groups or lightly crosslinked, for breaking oil-water emulsions derived from oilfield and oil refining operations.
For example, U.S. Patent Application Publication US 2007/0244248 discloses the use of a polymer containing aromatic and oleophilic groups for demulsifying oil-water emulsions. U.S. Pat. No. 5,100,582 discloses a very specific composition of tetrapolymer containing random combinations of acrylic acid, methacrylic acid, methyl methacrylate and butyl acrylate for use as demulsifying agent for water-in-crude oil.
Further, U.S. Pat. Nos. 6,025,426 and 5,330,650 each teach the use of hydrophilic cationic copolymers of acrylamide having high molecular weight as water clarification aids. U.S. Pat. No. 4,582,628 discloses the use of vinyl-type polymers, derived from hydrophilic and hydrophobic vinyl monomers, for demulsifying petroleum industry emulsions of oil and water.
Low molecular weight, water soluble, cationic polymers of dimethylaminoethyl acrylate methyl chloride and benzyl chloride quaternary salt are disclosed in U.S. Pat. No. 5,643,460 for breaking oil in water emulsions resulting from oilfield operations. U.S. Pat. No. 5,472,617 provides a method for demulsifying a crude oil and water emulsion which involves adding demulsifiers made from (meth)acrylates of oxyalkylates copolymerized with hydrophilic monomers.
Chinese Patent Application Publication CN1883740 discloses the use of polymers derived from hydrophobic (meth)acrylate ester monomers and hydrophilic (meth)acrylic acid monomers, and having molecular weights of 5,000 to 100,000 g/mol, for demulsifying crude oil and water emulsions.
None of the above-mentioned technologies utilizes hydrophobically modified, or surfactant modified, or lightly crosslinked anionic acrylate copolymers for separating oil and water dispersions or emulsions generated in connection with oilfield operations. It is believed that such anionic acrylate copolymers shall perform better than existing polymers used for demulsifying or clarifying such oil-water dispersions and emulsions.